You ran the same G/S table for both MAF and you say there is no difference? Are you scanning your PCM at all? Just because you don't feel a difference doesn't mean your fuel trims aren't pegged at max + or -, in either case your PE fueling will be shit and so will your economy, and I know that from experience. If you have a basic flash from some where, they usually are conservative on timing and pretty rich to keep people from blowing their stuff up. I've had lots of people bring me cars that were tuned like that.
There is a lot different in the table for the GM 75mm and the LQ4 maf, especially over 4000-5000 hz. Maybe it doesn't matter much on your application since you aren't moving enough air to get it up that high except under very heavy throttle, where Acceleration enrichment dumps make up for it, and you're not WOT long enough to completely lean out.
On my car typically @6300 rpm I'm hitting 11,300 hz on the Lq4 maf (gm 85mm) which is at the effective limit for my pcm (the MAF can go up to 15,000 but the pcm's table stops at 11,500 IIRC), so either i have to go to a larger MAF or scale the entire MAF signal and lose resolution.
A 1% change in your MAF value, will have a 3% change in your front O2 sensor reading.
IE, if I'm targeting .950 O2, and i have .880, it would mean i would want to increase the MAF cell that i was at during that o2 reading by ~2.6%... like wise, if your pcm is reading only a few percent off at any given range, it will had triple the effect on your o2 reading.
Changing your MAF sensor with out recalibrating the table will throw your entire tune off. Fuel trims is the cushion for this discrepancy, which can compensate up to 16%+ to 21%- (it can add 16% more fuel than what the table is calling for or remove 21%), but a change from the 75mm to the 85mm is outside of this range (on the + side). At wide open, if you were reaching the upper range of the MAF you would be ~6.5-7% too lean if your pcm is 'tuned' for the 75mm.